What a Difference a Day Makes--Abalone Pest is in the Dunk Tank

August 16, 2006

August 15, 2006

University of California biologists have found a way to nearly eliminate an invasive pest from California abalone production and display facilities.

The shell-dwelling fan worms (a sabellid polychaete) originated in South Africa and deform and reduce the marketability of abalone. The worms settle on the shells of abalone and other gastropods, which are a kind of sea snail, inhibiting and grossly deforming shell growth. Several native intertidal snails and slugs are susceptible to fan worm infestation.

The parasitic polychaete is a member of a group collectively known as sabellids or "fan worms." With funding from the UC Exotic/Invasive Pests and Diseases Research Program, UC Davis ecologist Ted Grosholz and UC Davis veterinarian James Moore found that submerging the fan worm in fresh water for 24 hours can destroy it. This practice allows aquaculturists and aquarium operators to destroy the fan worms in abalone holding units.

"The pest doesn't affect the abalone's meat, but damages the shell so much that the abalone's growth slows or virtually stops," says Grosholz. "Though the industry has learned to manage the pest, concerns over its impact and its potential spread have become widespread."

After sampling studies in 20 California locations that are known to have been exposed, or may have been exposed to sabellid-infested abalone, Moore and Grosholz found that sabellids have not become established in intertidal gastropod populations anywhere in California.

Abalone is highly prized in many cultures and is considered a delicacy in certain parts of Asia, especially in China and Japan. The inner shell of abalone is lined in an iridescent green, blue or pink sheen, which is a source of mother-of-pearl.

Because of its popularity, abalone has been depleted in many locations, including the coast of California. These declines, coupled with the value of abalone meat on the world market, have promoted the concept of abalone aquaculture internationally to supplement the world supply of abalone. Facilities free of fan worms are advised not to obtain abalone for stocking from facilities where this pest has been observed.

This research provides resource managers information on whether fan worm infestations are present among native intertidal snail populations. "Our sabellid transmission studies demonstrate that infestations can be sustained in a variety of sea snails, so the threat of such infestations becoming established in a particular location is real," says Moore.

"We recommend a 24-hour minimum fresh-water-immersion exposure time to destroy all life stages of the sabellid polychaete," says Moore. "This amount of time is recommended for field applications such as sanitizing a production tank after one group of abalone is moved out and before another is moved in."

The research team found that transmission of fan worms from one turban snail to another could occur, although the rate of transmission is very much lower than the rate between abalone. Turban snails can support fan worm infestations although they are less susceptible than abalone.

In a separate series of experiments, Moore's research team found the minimum fresh-water-exposure time necessary to kill mobile fan worm larvae is one minute. They recommend using a biocide such as chlorine to sanitize hands and tools when working in different production areas or display tanks.

The scientists produced a DVD describing the polychaete, the threat it poses and recommended techniques for preventing sabellid acquisition and transmission. The DVD, which contains both English and Spanish versions, will be distributed to abalone culturists and display facilities.